The disclosed technology relates generally to composite silicon or composite tin particles used to store lithium such as in a rechargeable lithium battery. Traditionally, batteries used graphite or other carbon based composites as anode material. Graphitic carbon has historically performed well due to its low voltage vs. lithium, high conductivity, decent cycle life and wide availability. However, for the performance of lithium ion batteries to be further improved, it is essential to realize an economic material capable of storing greater amounts of lithium and provide a higher energy density and specific capacity than graphite. More recently batteries have started using Sn and Si based anodes by mixing these with different metals or alloys with carbon to make composites.
There are several classes of Si and Sn materials. For example, one class of Si material is formed using an etching method to produce porous silicon. This etching method using hard acids such as HF/HNO3 to make pores in pure silicon crystals. Other etching methods etch pure silicon to make porous three-dimensional silicon particles used in High-Performance Lithium Secondary Batteries. Again these etching methods use an HF acid.
Another class of Si can be nano-crystallites. These nano-crystallites may be formed by ultra-fast cooling a melt of an aluminum alloy and then performing two etching steps. The first is to etch the aluminum away from the silicon and then, second, etch voids into clusters of the nano-crystallites. Another class of silicon based anode materials is formed by creating a metal matrix or metal compound coating around the silicon materials. This class of Si may be used as a negative active material for rechargeable lithium battery.